This invention relates to a luminescent material and an organic electroluminescent element and, more particularly, to an organic electroluminescent element material (EL material) which is used as a luminescent body in a variety of displays and to an organic electroluminescent element (EL element) prepared from said EL material.
An EL element utilizing electroluminescence is characterized by its high visibility because of self-luminescence and by its high impact resistance because of its being a completely solid element and is used in a thin display element, back light of a liquid crystal display and planar light source.
Some of known EL elements use a diamine derivative in the hole transporting layer and a complex of aluminum and 8-hydroxyquinoline (hereinafter referred to as Alq3) in the luminescent layer and emit green light at low direct-current voltage [Appl. Phys. Lett., 51, 913 (1987)]. Moreover, it is disclosed that the color of electroluminescence can be changed from green to yellow or red by the use of Alq3 alone [J. Appl. Phys. 65 (9), May (1989)].
The luminescent layer of EL elements which are currently in practical use is prepared as film from materials of low molecular weight by the technique of vacuum deposition while using Alq3 and the like as a luminescent material. In 1990, Burroughes et al. at the Cambridge University succeeded in observing an occurrence of electroluminescence from poly(p-phenylvinylene); induced with this success, the subject of high-molecular-weight EL materials is now receiving vigorous investigation. It is the film-making technique that will gain the greatest advantage from replacement of a low-molecular-weight material in the organic layer with a high-molecular-weight material: that is, a high-molecular-weight material in solution can be made into film by such coating technique as spin coating, dip coating and ink jet printing. Advantages of coating over vacuum deposition are, for example, ease of film making over a large-area substrate, low cost of a film-making apparatus and a short film-making time. However, high-molecular-weight materials generally have difficult problems in control of molecular weight and in purification. Metal complexes containing a ligand of an 8-aminoquinoline skeleton (JP2-255790 A) and compounds containing a ligand of oxazole ring or phenylpyridine ring (Toyota Central R and D Labs, Inc., R and D Review, Vol. 33, No. 2, pp. 3-21, June, 1998) have been reported, but they have not yielded high-performance elements emitting blue light.
Accordingly, an object of this invention is to provide a low-molecular-weight EL material which shows fluorescent quality comparable to that of the aforementioned Alq3 in the solid state and is soluble in an organic solvent such as chloroform and toluene. Another object of this invention is to provide an EL element prepared from the aforementioned EL material. A further object of this invention is to provide an EL material which emits blue fluorescent light with its principal wavelength located in the vicinity of 450 nm.
This invention relates to an organic electroluminescent element material represented by general formula (1). 
wherein Ar1 is a group represented by the following formula (2) and Ar2 is a group represented by the following formula (3) or (4) and, in case Ar2 is represented by formula (3), Ar1 and Ar2 may condense to form a 10-membered ring. 
In formulas (2), (3) and (4), R1-R4 are independently hydrogen, halogen, an alkyl group with 1-6 carbon atoms, an alkoxy group with 1-6 carbon atoms, an aryloxy group with 6-18 carbon atoms, phenyl group, a substituted phenyl group with up to 18 carbon atoms, amino group, a substituted amino group or hydroxyl group and R1 and R2 or R3 and R4 in adjacent position may link together to form a saturated or unsaturated 5- or 6-membered ring. The group R5 is hydrogen, an alkyl group with 1-16 carbon atoms, an alkoxy group with 1-6 carbon atoms, an aryloxy group with 6-18 carbon atoms, an alkyl group with 1-16 carbon atoms optionally containing a substituent selected from phenyl, amino, cyano, nitro, hydroxyl and halogen, an aryl group with 6-20 carbon atoms or an aralkyl group with 7-20 carbon atoms; in case Ar1 and Ar2 condense to form a 10-membered ring, R5 is an alkyl group with 6-16 carbon atoms optionally containing 1 or more of the aforementioned substituents, an aryl group with 6-20 carbon atoms or an aralkyl group with 7-20 carbon atoms. The group X is O or S, Z is a metal linked to N in formula (1) and to N constituting the hetero ring of Ar2 and is a divalent or trivalent metal selected from zinc, aluminum, copper, beryllium, ruthenium, cobalt, rhodium, iridium and platinum and n is 2 or 3.
El materials represented by the aforementioned formula (1) include compounds represented by the following general formulas (5), (6) and (7). 
Moreover, this invention relates to an EL element which contains the aforementioned EL material between two electrodes at least one of which is transparent. Still more, this invention relates to an EL element which contains at least one kind of the aforementioned EL material in its luminescent or electron transporting layer.
The EL materials of this invention are represented by the aforementioned general formula (1) and comprise the compounds represented by the aforementioned general formulas (5), (6) and (7).
The symbols in the aforementioned general formulas (5), (6) and (7) are the same as those in the aforementioned general formulas (1) to (4). However, R5 is preferably a group with 6 or more carbon atoms from the viewpoint of solvent solubility; for example, an alkyl group with 6-16 carbon atoms optionally containing one or more of the aforementioned substituents, an aryl group with 6-20 carbon atoms and an aryl group with 7-20 carbon atoms. In particular, R5 is preferably an alkyl group with 6-16 carbon atoms in a compound represented by formula (7).
The compounds represented by the aforementioned general formula (1) can be prepared by a variety of known methods; the following method is cited as an example.
An amine is treated with a sulfonyl chloride in pyridine and the reaction product is treated with a metal sulfate in alcohol. 
The compounds represented by the aforementioned general formula (5) can also be prepared by a variety of known methods. 2-Tributylstannylpyridine or its derivative is coupled with 2-iodonitrobenzene or its derivative and the nitro group is reduced to amino group. Thereafter, the resulting amine is treated with a variety of sulfonyl chlorides in pyridine and the reaction product is treated with a metal sulfate in alcohol. An example is shown below. 
Likewise, the compounds represented by the aforementioned general formula (6) can be prepared by a variety of known methods. Anthranilic acid or its derivative is coupled with ortho-aminophenol or its derivative and the coupled product is treated with a variety of sulfonyl chlorides in pyridine and the reaction product is treated with a metal sulfate in alcohol to give a product represented by formula (6). An example is shown below. 
The compounds represented by the aforementioned general formula (7) can be prepared by a variety of known methods. 8-Aminoquinoline or its derivative is treated with a variety of sulfonyl chlorides in pyridine and the reaction product is treated with a metal sulfate in alcohol to give a product represented by general formula (7). 
In the aforementioned general formulas (1) to (7), R1-R4, R5, X, Z and n are as defined above. Preferable as R1-R4 are hydrogen, halogen or a lower alkyl group (with 5 or less carbon atoms). Moreover, two of R1-R4 are preferably hydrogen. In case at least two of R1-R4 in adjacent position link together to form a ring, preferably a benzene ring, the new benzene ring condenses with the existing benzene ring bearing the two in question to form a naphthalene ring. Suitable for R5 are hydrogen, an alkyl group with 1-16 carbon atoms, an aryl group with 6-20 carbon atoms such as phenyl group, a substituted phenyl group containing 1 or 2 alkyl groups, biphenylyl and naphthyl, an aralkyl group with 7-20 carbon atoms and the foregoing aryl, alkyl and aralkyl groups containing 1 or 2 substituents selected from alkyl groups with 1-16 carbon atoms, alkoxy groups with 1-6 carbon atoms, aryloxy groups with 6-18 carbon atoms, phenyl, amino, cyano, nitro, hydroxyl and halogen. Here, R5 in the compounds represented by formula (7) contains 6 or more carbon atoms, and in case the substituent contains carbon, the number of carbon atoms of R5 is calculated by adding the number of carbon atoms in the substituent. Preferably, R5 is an aryl, alkyl or aralkyl group with 6-16 carbon atoms, X is O or S and Z is Zn or Al. The symbol n is 2 or 3 corresponding to the valence of Z.
Concrete examples of the compounds represented by the aforementioned general formula (1) are shown below, but this invention is not limited to them. 
Of the compounds exemplified above, the following are preferable: zinc bis-2-(2-(p-toluenesulfonamido)phenyl)pyridinate, zinc bis-2-(2-(n-octylsulfonamido)phenyl)pyridinate, zinc bis-8-(n-octylsulfonamido)quinolinate, zinc bis-2-(2-(p-toluenesulfonamido)phenyl)benzoxazolate, zinc bis-2-(2-(p-toluenesulfonamido)phenyl)benzothiazolate, zinc bis-2-(2-(n-octylsulfonamido)phenyl)benzoxazolate and zinc bis-2-(2-(n-octylsulfonamido)phenyl)benzothiazolate.
The organic metal complexes represented by the aforementioned general formula (1) are effective as EL materials, particularly as luminescent materials or electron transporting materials in EL elements.
An EL element should have an organic luminescent layer as an essential constituent layer between a pair of electrodes at least one of which is transparent and is subject to no other restriction. For example, an arrangement of an organic luminescent layer, a hole injecting layer and an electron transporting layer interposed between a pair of electrodes is cited as a desirable structure.
Concrete examples of the structures of this kind include the following;
a) anode/organic luminescent layer/cathode
b) anode/hole transporting layer/organic luminescent layer/cathode
c) anode/hole injecting layer/hole transporting layer/organic luminescent layer/cathode
d) anode/organic luminescent layer/electron transporting layer/cathode
e) anode/organic luminescent layer/electron transporting layer/electron injecting layer/cathode
f) anode/hole transporting layer/organic luminescent layer/electron transporting layer/cathode
g) anode/hole injecting layer/hole transporting layer/organic luminescent layer/electron transporting layer/cathode
h) anode/hole injecting layer/hole transporting layer/organic luminescent layer/electron transporting layer/electron injecting layer/cathode.
A light-absorbing diffusion layer may be interposed if necessary. Because of their excellent electron transporting and light emitting performance, the aforementioned EL materials are advantageously used in the electron transporting layer or organic luminescent layer, particularly in the organic luminescent layer. Furthermore, EL materials of this invention can be used singly or as a mixture of two kinds or more.
In the preparation of a luminescent layer from an EL material or a metal complex of this invention, an EL material represented by general formula (1) is made into thin film by a known technique such as spin coating and casting and, besides, patterning by ink jet printing is expected to become feasible. The conventional technique of vapor deposition can naturally be used for making thin film. The film thickness is preferably 10-1,000 nm, more preferably 20-200 nm.
Likewise, in the preparation of an electron transporting layer, the compound in question is made into thin film by a known technique such as spin coating, casting, ink jet printing and vapor deposition. The film thickness is preferably 10-1,000 nm, more preferably 20-200 nm.
The substrate that supports the aforementioned structural elements should meet the requirements for mechanical and thermal strength and transparency, but no other, and examples include plates of glass such as soda glass, non-fluorescent glass, phosphate glass and silicate glass, quartz, plates or films of plastics such as acrylic resins, polyethylene, polyesters and silicones, plates and foils of metals such as alumina and other known materials.
Materials for the anode include metals, alloys and electrically conductive compounds, all of a high work function, and their mixtures. Concrete examples are gold, CuI, indium tin oxide (ITO), SnO2, ZnO and other known materials.
Materials for the cathode include metals, alloys and electrically conductive compounds, all of a low work function, and their mixtures. Concrete examples are Na, Naxe2x80x94K alloy, Mg, Li, Mgxe2x80x94Al alloy, Alxe2x80x94AlO2, In, rare earth metals and other known materials.
Since at least one of the aforementioned electrodes allows the emitted light to emerge, that electrode needs to be transparent or translucent and the transmission of the side from which light emerges is preferably made 10% or more.
Materials useful for the hole transporting layer include aromatic amine derivatives, porphyrin derivatives, phthalocyanine compounds, poly(vinylcarbazole) and other known compounds.
Materials useful for the hole injecting layer include triazole compounds, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, oxazole derivatives, styrylanthracene derivatives, fluorene derivatives, hydrozone derivatives, stilbene derivatives, porphyrin derivatives, organic tertiary amine compounds, tetraphenylbenzidine derivatives and other known compounds. Particularly preferable are porphyrin compounds, tertiary amine compounds and styrylamine compounds.
Materials forming the electron injecting layer or the electron transporting layer or compounds exhibiting electron transporting capability and useful for the electron injecting material or the electron transporting material (may occasionally be present in the luminescent layer or elsewhere) include LiF, Alq3 and its derivatives, nitro-substituted fluorenone derivatives, thiopyran dioxide derivatives, diphenoquinone derivatives, perylene tetracarboxyl derivatives, anthraquinodimethan derivatives, fluorenylidenemethane derivatives, anthrone derivatives, oxadiazole derivatives, perinone derivatives, quinoline derivatives and other known compounds besides the EL materials of this invention.
In order to improve the heat resistance of the aforementioned layers of organic compounds such as the hole injecting layer, hole transporting layer and electron injecting layer, it is allowable to introduce polymerizable substituents to those organic compounds which constitute these layers and polymerize the substituted compounds before, during or after the formation of film.